It is generally known that by adding an inorganic or organic pigment capable of absorbing light having wavelengths in a specific range to a glass lens for spectacles, it is possible to improve anti-glare properties and visibility of the lens.
Sunglasses are used to adjust the transmittance of the sunlight, which includes light rays harmful to the eyes and can cause glare to the eyes. In order to reduce glare, it is important to reduce the transmittance of light having wavelengths near the center wavelength of the standard relative luminosity curve.
Ordinary sunglasses typically reduce transmittance over the entire wavelength range, and thus tend to extremely darken the field of view where the ambient light is scarce such as in twilight to such an extent that the wearer can hardly recognize surrounding objects (such as traffic signals and fishing floats). In other words, these sunglasses reduce entire light transmittance too much due to the effort to reduce glare and do not enable the wearer to adequately recognize subjects.
Sunglasses which can reduce transmittance of wavelengths near the center wavelength of the standard relative luminosity curve while maintaining overall brightness include those containing neodymium in the glass lenses which serves to absorb light having wavelengths near 580 nm.
Inorganic pigments that can block visible light having wavelengths near 585 nm when added in glass spectacle lenses include neodymium pigment compounds, which supply neodymium ions. Specific neodymium pigment compounds include anhydrides and hydrates of e.g. neodymium acetate, neodymium chloride, neodymium nitrate, neodymium oxide, neodymium-2,4-pentanedionate, neodymium trifluoropentanedionate, neodymium fluoride, and neodymium sulfate (JP Patent Publication 9-188796A (see e.g. paragraph 0012)).
Organic pigments which can, as with the neodymium pigment compounds, block visible light having wavelengths near 585 nm include a tetraazaporphyrin compound. This compound was added by 0.0002 to 0.05% by weight to plastic lenses (JP Patent Publication 2008-134618A (see e.g. claims 4, 6 and 8, and paragraph 0069)).
Further, a glass lens is known which comprises two glass lens substrates laminated together through a polymer film layer using an adhesive containing an ultraviolet absorbent which can absorb light having wavelengths of about 400 nm or less, such as benzotriazole (BTA) (JP Patent Publication 2004-279512A).
But in the invention of JP Patent Publication 2008-134618A, in which a tetraazaporphyrin compound is added to improve anti-glare properties, the lens materials to which this compound can be added are practically limited to plastic materials, of which the melting points are relatively low, and it was impossible to directly add this compound to glass lenses, which are generally used for spectacles.
This is because a tetraazaporphyrin compound would be thermally decomposed during melt-forming of a glass material. Such a thermally decomposed tetraazaporphyrin compound cannot sufficiently block light having wavelengths near 585 nm.
Also, the inventors of the present application tried to add a tetraazaporphyrin compound to the adhesive. But they encountered many problems in adding this compound to a very thin adhesive layer formed between the two lens substrates.
In order for a tetraazaporphyrin compound to perform its inherent function of absorbing light having wavelengths in a predetermined range when this compound is added to spectacle or sunglass lenses, it is necessary to add this compound to an extremely thin adhesive layer in a sufficiently high concentration. But this was difficult because a tetraazaporphyrin compound is less likely to be dissolved into an adhesive for glass lenses.
In order to prevent the lens obtained from becoming practically useless due to color phase irregularity, it is necessary to add the tetraazaporphyrin compound to an extremely thin adhesive layer in a sufficiently high concentration in a uniformly dispersed state. But this was difficult because a tetraazaporphyrin compound is less likely to be dissolved into an adhesive for glass lenses.